Novel Robust Folded Thermally Activated Delayed Fluorescence Molecules for High‐Performance OLEDs

Abstract

ABSTRACT Folded thermally activated delayed fluorescence (TADF) molecules based on through‐space charge transfer (TSCT) have aroused increasing interest, but the electroluminescence (EL) efficiencies of most folded TADF molecules are still inferior, and their application as sensitizers for multi‐resonance TADF (MR‐TADF) emitters remains barely explored. Herein, two novel isomeric folded TADF molecules, f‐ TRZ‐1 and f‐ TRZ‐2, are constructed by using 2,4,6‐triphenyl‐1,3,5‐triazine (TRZ) as acceptor, 9‐phenylcarbazole (PC) as donor, and 11,12‐dihydroindolo[2,3‐a]carbazole (HIC) as bridge. They exhibit regular intramolecular packing structures with effective TSCT and enjoy ultrahigh thermal stability and balanced bipolar charge transport. Moreover, efficient organic light‐emitting diodes (OLEDs) are fabricated using f‐ TRZ‐1 and f‐ TRZ‐2 as emitters, achieving maximum external quantum efficiencies ( η ext,max ) of up to 28.9%. f‐ TRZ‐1 and f‐ TRZ‐2 can perform as efficient sensitizers for the green MR‐TADF emitter tCzphB‐Fl, and the prepared hyperfluorescence OLEDs exhibit outstanding EL performances, with improved η ext,max s of up to 37.8% and reduced efficiency roll‐offs. This work demonstrates the promising potential of these folded TADF molecules as emitters and sensitizers for the fabrication of high‐performance OLEDs.